Use this utility function to append GA's campaign (or any other parameters with a small modification) to all links in your email at once, in an efficient way which uses `DOMDocument::loadHTML` instead of using custom regex.

EmailCampaignParameters.php

<?php

/**
 * appending campaign parameters to every single link `<a href=''></a>`
 * in the given $bodyHtml
 *
 * @param type $bodyHtml
 */
public function appendCampaignPrameters($bodyHtml, $utmCampaign) {
    $newParams = [
        'utm_source' => 'email',
        'utm_medium' => 'email',
        'utm_campaign' => $utmCampaign
    ];
    $doc = new \DOMDocument();
    $internalErrors = libxml_use_internal_errors(true); //http://stackoverflow.com/a/10482622/905801
    $doc->loadHTML($bodyHtml);
    libxml_use_internal_errors($internalErrors);
    foreach ($doc->getElementsByTagName('a') as $link) {
        $url = parse_url($link->getAttribute('href'));
        $gets = $newParams;
        if (isset($url['query'])) {
            $query = [];
            parse_str($url['query'], $query);
            $gets = array_merge($query, $newParams);
        }
        $newHref = '';
        if (isset($url['scheme'])) {
            $newHref .= $url['scheme'] . '://';
        }
        if (isset($url['host'])) {
            $newHref .= $url['host'];
        }
        if (isset($url['port'])) {
            $newHref .= ':' . $url['port'];
        }
        if (isset($url['path'])) {
            $newHref .= $url['path'];
        }
        $newHref .= '?' . http_build_query($gets);
        if (isset($url['fragment'])) {
            $newHref .= '#' . $url['fragment'];
        }
        $link->setAttribute('href', $newHref);
    }
    return $doc->saveHTML();
}